I can confirm this. While plants cutting, i accidentally cut a probe wire of my digital temperature gauge before many years and sealed the patched part, which is under water, with hot glue. Works well since then.

Btw, could you post a picture from this nice light in action? I wonder how it looks like and in which position you use it in the tank?

I did some more research on hot glue. It is safe for your fish, but it hardens too much. Hot and cold cycles will lead to cracking. 100% silicone stays flexible but might not tolerate the heat of your light. Super Glue Gel is what most pros use for gluing aquarium decorations. Not sure if that would work for your light.

If you put 6 3W LEDs inside the hot melt without a way to dissipate the heat, the LEDs will quickly get very hot and soften the hot melt and/or burn and die. You need some way for heat to get out. Also: it is not quite right to simply hook a voltage source to the LEDs, normally a current limiting part is also needed.

Unfortunately your comments indicates you have not really read what I have written. You can't push 3W of power through an LED unless you provide some way for the heat to dissipate. That you had a 60W glue gun is completely irrelevant. Second, you need CURRENT regulation, not VOLTAGE regulation for LEDs to operate safely. Please read the comments before replying.

I like it!However, I would recommend using clear silicone instead of hot glue. EVA is a common material used in hot glue, there are two characteristics that make EVA less than ideal for encapsulation of a submersible electrical object, the first is that EVA is somewhat porous (technically it has a high diffusivity for water) and secondly the EVA will eventually release acetic acid which can corrode the electrical systems. Even for all that, almost every solar panel is manufactured with EVA as the binding agent. Although, it's normally sandwiched between PVA and Glass. My info comes from some science journal articles I was reading last year for my senior research project.but again, I do like your project, I even voted for you ;)